The present invention relates to a remote diaphragm assembly for use in the process control industry to couple a process control instrument to a process. More particularly, the present invention relates to a remote diaphragm assembly whose components are easily assembled via a press-fit connection.
Sometimes it is necessary to separate a process device, such as a pressure transmitter, from a process medium it is to measure. This may occur, for example, because the process medium is hazardous to the process device (corrosive, extremely hot, etc.) or inaccessible to the process device. In that case, a remote diaphragm assembly can be used to couple the process device to the process medium while the process device is located a safe distance away.
Remote diaphragm assemblies typically include a flexible diaphragm that couples a diaphragm seal of a pressure transmitter to the process medium contained in a process vessel via a capillary tube. The capillary tube may extend for several meters to safely separate the process device from the process. The capillary tube is filled with a fill fluid that is substantially incompressible and completely fills the cavities between the flexible diaphragm and the diaphragm seal. The diaphragm of the remote diaphragm assembly interfaces with the process medium through a process flange to which it is mounted and flexes in response to the pressure of the process medium. These flexes are transmitted through the fill fluid to the diaphragm seal of the process device. The resulting flexes of the diaphragm seal are then transmitted in a similar fashion to a sensor contained within the process device which produces a signal relating to the pressure of the process medium in response thereto.
The interface between the remote diaphragm assembly and the process flange is generally in accordance with a standard, such as the American National Standards Institute (ANSI), Deutsche Industrie-Norm (DIN), Japanese Industrial Standard (JIS), International organization for Standardization (ISO), or other suitable standard. In order to accommodate the various interface standards, remote diaphragm assemblies often include separate diaphragm member and mounting portion components. The diaphragm member includes the thin flexible diaphragm and the mounting portion is adapted to secure the diaphragm member to the process flange of the process vessel.
The diaphragm member and the mounting portion are typically assembled prior to mounting to the process flange. Current methods for assembling these components include the use of screws, welded retaining rings, interference fit via knurled surfaces, and other similar fastening techniques. These fastening techniques can lead to increased manufacturing costs due to the complexity of the machining and/or labor that is required to form the components. Additionally, these fastening methods require the use of additional equipment and/or a skilled technician to assemble the components of the remote diaphragm assembly, which further increases manufacturing costs.
The present invention is directed to a remote diaphragm assembly, for use in the process control industry, which includes a diaphragm member and a mounting portion which can be press-fit assembled. This press-fit feature relates to the ability to securely assemble the diaphragm member and the mounting portion together by hand (i.e. without the use of tools, screws, welds, etc.). The diaphragm member includes a flexible diaphragm and a first press-fit member receiving portion. The mounting portion includes a second press-fit member receiving portion, which, when aligned with the first press-fit member receiving portion, results in the formation of a press-fit member cavity that contains a press-fit member. The press-fit member engages the first and second press-fit member receiving portions to form a press-fit connection therebetween and couple the diaphragm member to the mounting portion. Also disclosed is a method for assembling the above-described remote diaphragm assembly. In the method, a diaphragm member and a mounting portion are provided. The diaphragm member includes a flexible diaphragm and a first press-fit member receiving portion and the mounting portion includes a second press-fit member receiving portion. Next, a press-fit member is secured within either the first or the second press-fit member receiving portion. Finally, the diaphragm member and the mounting portion are press-fit together, during which the press-fit member is temporarily compressed into an assembly position and then expanded into a locking position within a press-fit member cavity that is formed when the first and second press-fit member receiving portions are aligned.